The present invention relates to a magnetic circuit for an yttrium-iron garnet crystal resonator for an oscillator, formed by a first cylindrical pole piece comprising a coil provided around an axial core, and a second cylindrical pole piece having a flat bottom, the two cylindrical pole pieces being joined together so as to close the magnetic circuit and the yttrium-iron garnet crystal being positioned in a gap defined by an end of the axial core and that part of the flat bottom facing the end.
The invention is used with great advantage in the field of high-frequency oscillators having as a resonator an yttrium-iron garnet crystal, also known as YIG oscillator.
The magnetic circuits of the type described in the opening paragraph have the advantage that they can be readily produced in so far as the second pole piece has a flat bottom, which also enables easy positioning of the high-frequency circuit coupled to the YIG crystal, by fixing it on the flat bottom. However, these known magnetic circuits have the disadvantage that they have rather significant stray fields, as a result of which, at high frequencies, for example frequencies above 10 GHz, the frequency-current relationship in the coil is no longer linear since, because of the stray fields and saturation of the materials, it is necessary to pass through the coil a current which is larger than necessary. It is an object of the invention to obviate this disadvantage while maintaining the main advantages of the flat bottom.